A conventional biaxially oriented polypropylene synthetic paper (hereinafter referred to as synthetic paper) is a synthetic paper of a multi-layer laminated structure. The synthetic paper 10 with a three-layer structure, as shown in FIG. 1, is composed of an outermost paper layer (A1), a foamed middle layer (C1), and an innermost paper layer (E1) that are sequentially stacked. A manufacturing process thereof, as shown in FIG. 2, is to use three extruders (a1, c1, and e1) to form a three-layer laminated product of hot-melt state by squeezing the composition of each layer into a homo-T-die.
A synthetic paper 15 with a five-layer structure, as shown in FIG. 3, is composed of an outermost paper layer (A2), an upper resin layer (B2), a foamed middle layer (C2), a lower resin layer (D2), and an innermost paper layer (E2) that are sequentially stacked. The manufacturing process thereof, as shown in FIG. 4, is to use five extruders (a1, b1, c1, d1, and e1) to form a five-layer laminated product of hot-melt state by squeezing the composition of each layer into the homo-T-die.
The prepared hot-melt three-layer or five-layer laminated product is rapidly cooled by a cooling molding device 20, longitudinally extended 2.5 to 8 times by a longitudinal extension device 30, and transversely extended 2.5 to 8 times by a transverse extension device 40. After a high-frequency treatment of a corona treatment device 50, the surface tension is raised, and then a synthetic paper 10 with the three-layer structure or the synthetic paper 15 with the five-layer structure is collected with a coiler 60.
However, after nearly 20 years of development, the quality of the biaxially oriented polypropylene synthetic paper still has the disadvantage of uneven printing haze, so that it has not reached the goal of replacing natural paper products.